Stainless Steel Coil Tube (Coiltube) — Radiant Heating & Cooling System Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed for integration into radiant cooling and heating systems as well as Fan Coil Unit (FCU) with Fresh Air System (FAU) hybrid configurations. This product represents the core heat-transfer element in distributed thermal management systems used across commercial, industrial, and institutional building environments. The coil tube is manufactured to deliver optimal thermal conductivity, hydraulic efficiency, and long-term structural integrity under continuous cyclic operating conditions.
Wenzhou Jixing Metal Materials Co., Ltd supplies this product as part of a comprehensive material solution for HVAC (Heating, Ventilation, and Air Conditioning) engineering applications, where the coil tube serves as the primary medium for transferring thermal energy between circulating fluids and the conditioned space.
2. Material & Properties
2.1 Base Material
- Material Grade: Austenitic Stainless Steel (奥氏体不锈钢) — typically SUS304 (UNS S30400) or SUS316 (UNS S31600)
- Chemical Composition: Chromium (Cr) ≥ 18%, Nickel (Ni) ≥ 8%, Molybdenum (Mo) ≥ 2% (for 316 grade), Carbon (C) ≤ 0.08%
- Corrosion Resistance: Superior resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC) in aqueous environments
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing efficient heat exchange capability
- Operating Temperature Range: −196°C to +870°C
- Hygienic Surface Finish: Ra ≤ 0.4 μm (electropolished) for potable water and HVAC loop compatibility
2.2 Mechanical Properties
- Tensile Strength: ≥ 520 MPa (SUS304), ≥ 570 MPa (SUS316)
- Yield Strength: ≥ 205 MPa
- Elongation: ≥ 40% (A50mm)
- Hardness: ≤ 217 HB (annealed condition)
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Nominal Outer Diameter (OD) | Φ6.0 mm – Φ25.4 mm (1/8" – 1") | ASTM A269 / ASTM A213 |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm | ASTM A269 |
| Coil Diameter | Φ100 mm – Φ600 mm (adjustable per project) | Custom / OEM |
| Tube Length per Coil | 3 m – 50 m (continuous) | Project-specific |
| Surface Finish | 2B, BA (Bright Annealed), Electropolished | ASTM A479 |
| End Treatment | Flat-cut, Beveled, Threaded, or Fitted | ASME B36.19M |
| Maximum Working Pressure | ≤ 1.6 MPa (16 bar) at 90°C | EN 10216-5 |
| Tolerance on OD | ±0.05 mm – ±0.10 mm | ASTM A213 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Delivery Form | Coiled (盘管) / Straight Length | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip sourced from certified mills, verified via mill test certificates (MTC) conforming to EN 10204 3.1.
- Coil Forming (Coiling): Precision CNC-driven coiling machines wind the seamless or welded tube into uniform helical coils with controlled pitch and diameter tolerances.
- Welding (if applicable): TIG (Tungsten Inert Gas) welding with argon shielding for longitudinal seam integrity; weld penetration verified by radiographic testing (RT) or ultrasonic testing (UT).
- Heat Treatment: Solution annealing at 1050°C–1150°C followed by rapid quenching to achieve full austenitic microstructure and maximum corrosion resistance.
- Surface Finishing: Mechanical polishing or electropolishing to achieve specified surface roughness (Ra ≤ 0.4 μm), removing oxidation scale and enhancing hygienic properties.
- Quality Inspection: Dimensional verification, visual inspection (VT), pressure testing (hydrostatic at 1.5× working pressure), and optional spectrographic analysis for chemical composition confirmation.
- Packaging: Coils secured with protective wraps, moisture-absorbing desiccants, and labeled per ISO 7800 identification standards.
4.2 Process Advantages
- Continuous coil forming eliminates butt-weld joints, reducing failure points in circulating fluid systems.
- CNC-controlled coiling ensures uniform bend radius, preventing localized stress concentrations and kinking.
- Electropolished surfaces minimize biofilm adhesion, critical for long-duration HVAC loop operation.
5. Applications
5.1 Radiant Cooling & Heating Systems
The coil tube is embedded within ceiling panels, floor screeds, or wall cavities to provide distributed thermal exchange. In radiant cooling configurations, chilled water circulates through the coil at temperatures of 12°C–18°C, absorbing heat from the occupied zone. In radiant heating modes, warm water (35°C–55°C) provides low-temperature surface heating with minimal stratification losses.
5.2 Fan Coil Unit (FCU) + Fresh Air System (FAU) Hybrid Applications
In joint application systems, the stainless steel coil tube serves as the heat exchanger core within fan coil units. The hybrid architecture combines:
- FCU Coil: Dehumidification and sensible heat removal via the stainless steel coil tube bank.
- FAU Integration: Fresh air supply at controlled temperature and humidity, reducing the latent load on the coil.
- System Synergy: The stainless steel coil tube's corrosion resistance and thermal stability ensure reliable operation under variable duty cycles imposed by the dual-system control logic.
5.3 Additional Applications
- Commercial HVAC systems in hospitals, laboratories, and pharmaceutical facilities
- Food and beverage processing plant refrigeration loops
- Industrial process heat exchange (chemical, petrochemical)
- Geothermal heating/cooling distribution manifolds
- Marine HVAC and bilge cooling systems (SUS316 grade)
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (EU) | Conformity with European Product Safety Directives |
| ASTM A269 | Seamless and Welded Austenitic Stainless Steel Tubing |
| ASTM A213 | Seamless Austenitic Stainless Steel Heat-Exchanger and Heat-Sink Tubing |
| EN 10216-5 | Non-alloy and Alloy Steel Tubes — Technical Delivery Conditions (Austenitic) |
| EN 10217-7 | Non-alloy and Alloy Steel Tubes — Seamless Tubes for High-Pressure Boilers (Austenitic) |
| GB/T 12771 | Chinese National Standard — Seamless Stainless Steel Tubes for General Purposes |
| GB/T 14976 | Chinese National Standard — Cold-Drawn Seamless Stainless Steel Tubes |
7. Unique Selling Points
- Exceptional Corrosion Durability: Austenitic stainless steel construction eliminates internal corrosion scaling, maintaining heat transfer efficiency over the design life of 25+ years without degradation.
- Seamless Coil Integrity: Continuous coiling from seamless tubing eliminates longitudinal weld seams, providing uniform hydraulic performance and zero leak paths in closed-loop radiant systems.
- Hygienic Surface Quality: Electropolished finish (Ra ≤ 0.4 μm) prevents microbial colonization, making the product suitable for pharmaceutical, food-grade, and medical HVAC applications.
- Thermal Performance Stability: Low thermal expansion coefficient (16 μm/(m·°C)) ensures dimensional stability under thermal cycling, maintaining seal integrity at connection points.
- System Compatibility: Designed for seamless integration into both standalone radiant systems and hybrid FCU+FAU architectures, offering engineering flexibility for complex building climate control strategies.
- Full Traceability: Each coil batch is accompanied by a Material Test Certificate (MTC) per EN 10204 3.1, with heat number, chemical analysis, and mechanical test data for complete supply chain traceability.
8. Engineering Notes
In the joint application of radiant cooling/heating and FCU+FAU systems, the stainless steel coil tube must be specified with attention to the following design parameters: (1) Minimum bend radius ≥ 5× tube OD to prevent wall thinning at curvature; (2) Flow velocity maintained between 0.5 m/s and 1.5 m/s to balance heat transfer coefficient against erosion-corrosion risk; (3) Glycol-based antifreeze solutions limited to ≤ 30% concentration to avoid chloride-induced stress corrosion cracking in SUS304 grade; (4) System water quality maintained per ASHRAE Guideline 12 with total dissolved solids (TDS) ≤ 500 ppm.
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support, custom coil configurations, and post-delivery engineering consultation for all coil tube products supplied for radiant and FCU hybrid system applications.